Thirty years after a former Nasa scientist sounded the alarm for the general public about climate change and human activity, the expert issued a fresh warning that the world is failing “miserably” to deal with the worsening dangers.

While Donald Trump and many conservatives like to argue that climate change is a hoax, James Hansen, the 77-year-old former Nasa climate scientist, said in an interview at his home in New York that the relevant hoax today is perpetrated by those leaders claiming to be addressing the problem.

Hansen provided what’s considered the first warning to a mass audience about global warming when, in 1988, he told a US congressional hearing he could declare “with 99% confidence” that a recent sharp rise in temperatures was a result of human activity.

Since this time, the world’s greenhouse gas emissions have mushroomed despite repeated, increasingly frantic warnings about civilization-shaking catastrophe, from scientists amassing reams of evidence in Hansen’s wake.

“All we’ve done is agree there’s a problem,” Hansen told the Guardian. “We agreed that in 1992 [at the Earth summit in Rio] and re-agreed it again in Paris [at the 2015 climate accord]. We haven’t acknowledged what is required to solve it. Promises like Paris don’t mean much, it’s wishful thinking. It’s a hoax that governments have played on us since the 1990s.”

Hansen’s long list of culprits for this inertia are both familiar – the nefarious lobbying of the fossil fuel industry – and surprising. Jerry Brown, the progressive governor of California, and the German chancellor, Angela Merkel, are “both pretending to be solving the problem” while being unambitious and shunning low-carbon nuclear power, Hansen argues.

James Hansen: ‘Promises like Paris don’t mean much, it’s wishful thinking. It’s a hoax that governments have played on us since the 1990s.’ Photograph: Arrizabalaga/REX Shutterstock

There is particular scorn for Barack Obama. Hansen says in a scathing upcoming book that the former president “failed miserably” on climate change and oversaw policies that were “late, ineffectual and partisan”.

Hansen even accuses Obama of passing up the opportunity to thwart Donald Trump’s destruction of US climate action, by declining to settle a lawsuit the scientist, his granddaughter and 20 other young people are waging against the government, accusing it of unconstitutionally causing peril to their living environment.

“Near the end of his administration the US said it would reduce emissions 80% by 2050,” Hansen said.

“Our lawsuit demands a reduction of 6% a year so I thought, ‘That’s close enough, let’s settle the lawsuit.’ We got through to Obama’s office but he decided against it. It was a tremendous opportunity. This was after Trump’s election, so if we’d settled it quickly the US legally wouldn’t be able to do the absurd things Trump is doing now by opening up all sorts of fossil fuel sources.”

Hansen’s frustrations temper any satisfaction at largely being vindicated for his testimony, delivered to lawmakers on 23 June 1988.

Wearing a cream-coloured suit, the soft-spoken son of Iowan tenant farmers hunched over the microphone in Washington to explain that humans had entered a confronting new era. “The greenhouse effect has been detected and it is changing our climate now,” he said.

Afterwards, Hansen told reporters: “It is time to stop waffling so much and say that the evidence is pretty strong that the greenhouse effect is here.” He brandished new research that forecast that 1988 was set to be the warmest year on record, as well as projections for future heat under three different emissions scenarios. The world has dutifully followed Hansen’s “scenario B” – we are “smack on it” it, Hansen said last week – with global temperatures jumping by around 1C (1.8F) over the past century.

These findings hadn’t occurred in a vacuum, of course – the Irish physicist John Tyndall confirmed that carbon dioxide is a heat-trapping gas in the 1850s. A 1985 scientific conference in Villach, Austria, concluded the temperature rise in the 21st century would be “greater than in any man’s history”. The changes in motion would “affect life on Earth for centuries to come”, the New York Times warned the morning after Hansen’s testimony.

James Hansen testifies before a Senate transportation subcommittee on 8 May 1989, a year after his history-making testimony regarding climate change. Photograph: Dennis Cook/AP

Three decades of diplomacy has blossomed into an international consensus, albeit rattled by Trump, that the temperature rise must be curbed to “well below” 2C (3.6F) above pre-industrial times. But in this time emissions have soared (in 1988, 20bn tons of carbon dioxide was emitted – by 2017 it was 32bn tons) with promised cuts insufficient for the 2C goal. Despite the notable growth of renewable energy such as solar and wind, Hansen believes there is no pathway to salvation without a tax on carbon-producing fuels.

“The solution isn’t complicated, it’s not rocket science,” Hansen said. “Emissions aren’t going to go down if the cost of fossil fuels isn’t honest. Economists are very clear on this. We need a steadily increasing fee that is then distributed to the public.”

Hansen faced opposition even before his testimony – he recalls a Nasa colleague telling him on the morning of his presentation “no respectable scientist” would claim the world is warming – and faced subsequent meddling and censorship from George HW Bush’s administration.

He eventually retired from Nasa in 2013 and promptly reinvented himself as an activist who was arrested, wearing his trademark hat, outside the White House while protesting against the Keystone oil pipeline.

James Hansen is arrested outside the White House for protesting on 27 September 2010. Photograph: Alamy

The dawdling global response to warming temperatures means runaway climate change now looms. The aspirational 1.5C (2.7F) warming target set in Paris could be surpassed by 2040. Huge amounts of ice from western Antarctica are crashing into the ocean, redrawing forecasts for sea level rise. Some low-lying islands fear extinction.

“It’s not too late,” Hansen stressed. “There is a rate of reduction that’s feasible to stay well below 2C. But you just need that price on carbon.”

John Holdren, who was Obama’s chief science adviser, told the Guardian that the Paris agreement achieved what was possible without support from Congress and that legally binding lawsuits would be “problematic”.

However, he added that while he had reservations about Hansen’s policy ideas he was one of the “true giants” of climate science.

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“Poor Jim Hansen. He’s a tragic hero,” said Naomi Oreskes, a Harvard academic who studies the history of science. “The Cassandra aspect of his life is that he’s cursed to understand and diagnose what’s going on but unable to persuade people to do something about it. We are all raised to believe knowledge is power but Hansen proves the untruth of that slogan. Power is power.”

That power has been most aggressively wielded by fossil fuel companies such as Exxon and Shell which, despite being well aware of the dangers of climate change decades before Hansen’s touchstone moment in 1988, funded a network of groups that ridiculed the science and funded sympathetic politicians. Later, they were to be joined by the bulk of the US Republican party, which now recoils from any action on climate change as heresy.

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“Obama was committed to action but couldn’t do much with the Congress he had,” Oreskes said. “To blame the Democrats and Obama is to misunderstand the political context. There was a huge, organized network that put forward a message of confusion and doubt.”

Climate scientist Michael Oppenheimer, who testified at the same 1988 hearing about sea level rise, said the struggle to confront climate change has been “discouraging”.

“The nasty anti-science movement ramped up and now we are way behind.”

“I’m convinced we will deal with the problem,” he said. “[But] not before there is an amount of suffering that is unconscionable and should’ve been avoided.”